Variation of Parameters  Summary and Q&A
TL;DR
Using variation of parameters, we can solve linear differential equations by finding null solutions and integrating them with a source function.
Questions & Answers
Q: What is the purpose of variation of parameters in solving linear differential equations?
Variation of parameters is used to find a particular solution to a linear differential equation by incorporating null solutions and integrating them with a source function.
Q: How do we determine the conditions on the parameters in variation of parameters?
By plugging the particular solution form into the differential equation, we obtain two equations for the derivatives of the parameters. These equations involve the source function and can be solved to determine the conditions on the parameters.
Q: Can null solutions vary with time in variation of parameters?
While it is possible to find null solutions that vary with time, the most common and easier case is when the null solutions have constant coefficients.
Q: What is the significance of the Wronskian in variation of parameters?
The Wronskian is a determinant that plays a critical role in variation of parameters. Its value determines the denominator in the formula for the particular solution and ensures that the equations are independent and invertible.
Summary & Key Takeaways

Variation of parameters is a method to solve linear differential equations, specifically secondorder equations, by finding a particular solution.

To use variation of parameters, we need to know two null solutions that satisfy the equation with a zero righthand side.

By multiplying the null solutions by varying parameters, we can find a form of the solution and determine the conditions on the parameters by plugging them into the differential equation.

We end up with two equations for the derivatives of the parameters, which can be solved for each time instant, leading to the complete answer.